Filter element for filtering of liquids

ABSTRACT

A coiled strip of filter material includes a pair of superimposed longitudinally coextensive strip portions each having a longitudinally extending free edge and a transversely spaced connected edge connected with the respectively other strip portion. A plurality of at least substantially parallel transverse corrugations is provided in only one of these strip portions and the convolutions of the coiled strip define with one another two spirally intercalated internal filter chambers one of which is open at one axial end of the coil and the other of which is open at the other axial end of the coil.

United States Patent [1 1 Cub et al.

[ 11 3,739,916 [4 June 19, 1973 1 FILTER ELEMENT FOR FILTERING OFLIQUIDS [73] Assignee: Robert Bosch G.m.b.H., Stuttgart,

Germany [22] Filed: May 4, 1971 [2]] Appl. No.: 140,059

[30] Foreign Application Priority Data 668,101 2/1901 Hinde 161/133FOREIGN PATENTS OR APPLICATIONS 699,168 10/1953 Great Britain 210/494755,481 8/1956 Great Britain 210/494 1,222,727 6/1960 France 210/4931,094,978 5/1955 France 210/493 Primary ExaminerSamih N. ZaharnaAssistant ExaminerF. F. Calvetti Attorney-Michael S. Striker [57]ABSTRACT A coiled strip of filter material includes a pair ofsuperimposed longitudinally coextensive strip portions each having alongitudinally extending free edge and a transversely spaced connectededge connected with the respectively other strip portion. A plurality ofat least substantially parallel transverse corrugations is provided inonly one of these strip portions and the convolutions of the coiledstrip define with one another two spirally intercalated internal filterchambers one of which is open at one axial end of the coil and the otherof which is open at the other axial end of the coil.

9 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION The presentinvention relates generally to a filter element, and more particularlyto a filter element for filtering of liquids.

It is already known to provide a coiled filter element by convoluting astrip of filter material which is first folded to a substantiallyV-shaped configuration so as to have two superimposed strip portions,both of which are provided with transversely extending corrugationswhich serve to compensate for length variations in the individual stripportions during the convoluting of the filter strip to a coiledconfiguration.

In this prior-art construction the strip is first folded so as toprovide two superimposed strip portions, and is only then provided insuitable manner as by embossing or the like with the transverselyextending corrugations. The strip itself usually consists of paper andwhen the corrugations are formed the structure of the paper is affectedin both strip portions. This can be disadvantageous under certaincircumstances. Furthermore, the prior-art construction requiresadditional components for maintaining adjacent convolutions of thecoiled strip element spaced from one another to permit the flow ofliquid through the thus-obtained spaces. On one axial end adjacentconvultions are also connected with one another by a suitable adhesiveto provide two spirally intercalated filter chambers which are open fromopposite axial ends of the coil. However, in the prior-art constructionthecorrugated depressions in both strip portions of the filter stripmake it possible for accummulations of adhesive to occur locally whichis also undesirable. Finally, the provision of corrugations in bothstrip portions which are superimposed upon one another is more difficultand requires greater care in operation than this is necessary if thereare to be provided in only a strip or strip portions of single thicknessrather than dual thickness.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to further improve the aforementioned prior-art filterelement.

More particularly, it is an object of the present invention to providean improved filter element of the type here under discussion which isstill simpler than what is known from the art, which is therefore lessexpensive and which is fully satisfactory for the operationalrequirements which are made of it.

A concomitant object of the invention is to provide such an improvedfilter element which offers itself readily for manufacture by automatedproduction methods.

In pursuance of the above objects, and others'which will become apparenthereafter, one feature of the invention resides in a filter element forfiltering of liquids which, briefly stated, comprises a coiled strip offilter material including a pair of superimposed longitudinallycoextensive strip portions each having a longitudinally extending freeedge and a transversely spaced connected edge connected with therespectively other strip portion. A plurality of at least substantiallyparallel transverse corrugations are provided in only one of these stripportions and the convolutions of the coiled strip define two spirallyintercalated internal filter chambers one of which is open at one axialend of the coil and the other of which is open at the other axial end ofthe coil. The corrugations compensate for length variations in one ofthe strip portions relative to the other strip portion which occur dueto convoluting of the strip to coiled shape.

Thefact that in the filter element of the present invention only one ofthe strip portions is provided with corrugations does not mean that theother strip portion need be entirely smooth or planar. However,according to the invention it will not be provided with corrugations asis the other strip portion.

By resorting to the construction according to the present invention,several advantages are obtained. Firstly, when the corrugations areformed only the paper structure of the one strip it is understood thatthe strip will normally be again made of paper will be affected by theprovision of the corrugations, whereas the paper structure of the otherstrip portion remains unchanged. The corrugations still serve thepurpose of providing a compensation for length variations which occurbetween the respective strip portions during convoluting of the strip tocoil shape. In addition, however, the corrugations in the one stripportion in conjunction with the fact that the other stripportion is notprovided with such corrugations, serve thus to act in effect as spacersmaintaining adjacent convolutions spaced from one another and alsomaintaining the strip portions spaced from one another, withoutrequiring separate components for this purpose as is known from theprior art. In addition, the corrugations reinforce the material of thestrip, making it possible to readily roll the strip composed of thesuperimposed strip portions to spiral configuration without requiringany auxiliary supporting components. Because of the regular and evendistribution of the corrugations, the application of adhesive for thepurposes and in the manner already discussed, and still to be discussedfurther below, can be properly carried out without the localaccumulation of excessive quantities of such adhesive, whereby theoverall use of the adhesive is reduced. Because it is not necessary toprovide separate spacing components in the coil, more filter paper canbe provided in form of the strip in a predetermined volume of a coilthan this is possible in accordance with the prior art. This means, forinstance, that is a predetermined filter surface area is specified, thevolume of the coil can be reduced.

It is particularly advantageous if that portion or strip portion whichis provided with corrugations has a marginal section which is foldedback upon the strip portion in question and extends along the free edgeof the latter. In this manner, the free edge is reinforced and stiffenedagainst bending, an advantage particularly with reference to adhesiveconnecting of adjacent convolutions of the strip in the coil madetherefrom.

It is also advantageous if the strip is so convoluted to coil form thatthe strip portion provided with the corrugations faces inwardly towardsthe center of the coil whereas the non-corrugated strip portion facesoutwardly away from the center. The advantage here is that during theconvoluting the strip portion provided with the corrugations (and whichis therefore readily yeildable) is subjected to the pressure resultingfrom the winding or convoluting operation. This means that for obtaininga predetermined depth of the corrugations in the completed filterelement, the depth of the corrugations formed in the strip prior toconvoluting of the same, can be smaller that would otherwise bepossible.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction'and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIG. is a perspective viewillustrating a filter element according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing itwill be seen that the coiled filter element is identified in toto withreference numeral 1. Because the outer free end of the coiled elementhas been shown loosened from the remainder of the element, it is clearlyvisible that the element is composed of an elongated strip 2 whichconventionally consists of filter paper and which is folded in half insubstantially V-shaped configuration to provide two strip portions 5 andwhich are longitudinally coextensive. The strip portion 5 is providedwith a plurality of longitudinally arrayed transversely extendingcorrugations 6 which extend over the entire width of the strip portion 5and which are arranged at regular intervals normal to the foldong edge 7at which the strip portions 5 and 10 are connected with one another. Thestrip 1 is wound onto a center tubular element 4, which may for instanceconsist of cardboard or the like, and adjacent ones of its convolutionsare tightly and firmly connected with a thermoplastic adhesive 3.

Each of the strip portions 5 and 10 has a free edge transversely spacedfrom the respective connected edge extending along the fold 7, and thefree edge 8 of the strip portion 5 is provided with a marginal section 9which is folded back upon a corresponding section of the strip portion 5so as in this embodiment to be located between the strip portion 5 andthe strip portion 10. The latter is essentially smooth, and not providedwith corrugations, whereas the marginal section 9 provided with the samecorrugations as the remainder of the strip portion 5 and serves thepurpose of reinforcing and stiffening the edge 8, making thecorrugations 6 in this area resistant to deformation.

As the drawing shows, a strip of a thermoplastic adhesive 3 which may beof suitable and already well known type is arranged in the region of thefree edge 8 between the corrugated strip portion 5 of any oneconvolution and the cooperating smooth strip portion 10 of the adjacentconvolution of the spirally convoluted strip 2. The purpose is toprovide in the coil 1 two spirally intercalated filter pockets 11 and 12one of which is open to and accessible from the axial end 13 whereas theother is open to and accessible from the axial end 14 of the coil. Thechambers 11 and 12 are completely separated from one another. Due to theprovision of the section 9 between the strip portions 5 and 10, thechamber 11 has a larger volume than the chamber 12 to thereby provideadequate space for the deposition and retention of contaminants in aliquid which is to be filtered with the novel filter element, thusreducing the danger that the filter element might become clogged.

Of course, in conventional manner the filter element 1 will be insertedinto a housing provided customarily for such filter elements, and sealedso that the axial end 13 is connected with a supply conduit and theaxial end 14 with a withdrawal conduit. Intermediate these conduits theliquid to be filtered passes through the filter element 1 and isfiltered.

To produce the novel filter element according to the present invention,a strip of suitable filter paper is first folded back upon itself alonga section adjacent an edge, to thereby form the section 9. Subsequently,the portion 5 provided with the section 9 is provided with corrugationsextending transversely to the elongation of the strip and to thelongitudinal center line thereof. corrugations 6 which areadvantageously provided by passing the strip through a pair of cammingand bossing gears which of course act only upon that half of the stripcorresponding later to the strip portions 5. Subsequently the strip isfolded transversely to substantially V-shaped configuration in order toobtain the two strip portions 5 and 10. Now, it is spirally convolutedabout the center tubular element 4, and the thermoplastic adhesive 3 isinserted between adjacent convolutions as the coil is being fonned.

It is advantageous for the thermoplastic adhesive 3 to be supplied inviscous state through a nozzle onto the smooth strip portion 10 adjacentthe free edge thereof, and to be pressed into the corrugations 6 duringthe convoluting so that it will solidify in these corrugations as it isallowed to cool off. The use of such a material makes it possible toobtain a seal-tight and also a strong connection between the two stripportions 5 and 10 even when they are spaced relatively far fron oneanother. Also, this material does not shrink on cooling and ischemically resistant particularly to liquid fuels.

The beginning end which is secured to the center tubular element 4 andthe terminal end which is shown loose in the drawing are each sealed byan additional quantity of thermoplastic adhesive 3 extending along linesparallel to the corrugations 6. The sealing and the tearing of the firstor innermost convolution with reference to the tubular element 4 isachieved in that an increased quantity of thermoplastic material isapplied precisely over the edge of the first convolution during thewinding process, so that as the second convolution is wound over thefirst convolution, the grooves between the layers are filled and aresidual quantity of the adhesive is pressed out at the axial end of thecoil but in still highly viscous state, where it is engaged by means ofspecial tools and is pushed axially into the first two coils to beallowed to cool in order to obtain a bounding and sealing action. Havingthe sec tion 9 be located between the strip portions 5 and 10 assuresduring the winding of the strip 2 to the illustrated coil that thesection 9 is compressed less in radial direction than the strip portion5 with the corrugations 6 and will thus properly overlye the adjacentsurface portions of the strp portions 5.

The drawing illustrates the corrugations 6 to be of uniformcross-sectional configuration throughout. However, according to afurther embodiment of the invention, it is also possible to soconfigurate the cross section of the corrugations 6 that in the regionof the free edge 8 of the strip portion 5 they are larger so that thecombined cross-sectional areas of the open ends of the corrugationslocated at the axial end 13 which is the inlet end of the finishedfilter element, is greater than the combined cross-sectional area of theends of those corrugations which are sealed by the thermoplasticadhesive 3. Even if this embodiment is chosen, however, the function ofthe corrugations 6 as spaces, as reinforcements, and forlength-compensating purposes remains unaffected. it goes without sayingthat it is also possible to continuously vary the cross-sectionalconfiguration of the corrugations 6, from the free edge 8 to or towardsthe fold 7. It will also be appreciated that according to an additionalembodiment it is possible to have the corrugations 6 provided in thestrip portion 10 and to have the strip portion 5 be smooth, which is tosay that the strip 2 can be so wound that the strip portion providedwith the corrugations will face outwardly away from the center tubularelement 4 and the strip portion which is smooth will face inwardlytowards this element. It is preferred to use as the starting materialfor the strip 2 a so-called crepe paper which is then further processedin the manner discussed above. However, it is of course equally wellpossible to use smooth non-creped paper and to process it further in themanner discussed above.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in afilter element for filtering of liquids, it is not intended to belimited to the details shown, since various modifications and structuralchanges may be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledgereadily adapt it for various applications without omitting features,that, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. A filter element for filtering of liquids, comprising a strip offilter material folded so as to form two closely adjacent strip portionsconsisting of one piece and having aligned longitudinally extending freeedges and longitudinally extending second edges transversely spaced fromthe respective free edges, said strip portions being, due to saidfolding, unitary along said second edges only and said strip beingcoiled so that each of said strip portions forms a plurality ofconvolutions which alternate with the convolutions of the other stripportion, only one of said strip portions having a plurality of at leastsubstantially parallel transverse corrugations which compensate forlength variations due to coiling of said strip, the convolutions of saidstrip portions defining two spirally intercalated internal filterchambers one of which is open in the region of said free edges andclosed in the region of said second edges due to said strip portionsbeing folded and therefore unitary along said second edges; and meansfor closing the other of said intercalated internal filter chambersalong said free edges of said strip portions, so that said intercalatedinternal filter chambers are open and closed along opposite edge of saidstrip portions, respectively.

2. A filter element as defined in claim 1, said one strip portionincluding a marginal section extending along said free edge and foldedback upon a corresponding section of said one strip portion.

3. A filter element as defined in claim 1, said one strip portion facinginwardly toward the center of the coiled strip and the other of saidstrip portions facing outwardly away from said center.

4. A filter element as defined in claim 3, said one strip portionincluding a marginal section extending along said free edge and foldedback upon a corresponding section of said one strip portion so as to belocated between the latter and the other of said strip portions.

5. A filter element as defined in claim 1, wherein the combinedcross-sectional area of said open end of said other corrugations exceedsthe combined crosssectional area of said open ends of said somecorrugations.

6. A filter element as defined in claim 1, said corrugations forming inthe region of said free edge of said one strip portion a uniformlysinuous configuration.

7. A filter element as defined in claim 1; further comprising a tubularcenter element about which said strip is convoluted; and adhesive meanssealingly connecting the initial convolution of said strip with saidcenter element.

8. A filter element as defined in claim 7, wherein said adhesive meansis thermoplastic means sealingly connecting said initial convolutionwith said center ele ment at the opposite axial ends thereof.

9. A filter element as defined in claim 7, wherein said tubular centerelement is a cardboard tube.

1. A filter element for filtering of liquids, comprising a strip offilter material folded so as to form two closely adjacent strip portionsconsisting of one piece and having aligned longitudinally extending freeedges and longitudinally extending second edges transversely spaced fromthe respective free edges, said strip portions being, due to saidfolding, unitary along said second edges only and said strip beingcoiled so that each of said strip portions forms a plurality ofconvolutions which alternate with the convolutions of the other stripportion, only one of said strip portions having a plurality of at leastsubstantially parallel transverse corrugations which compensate forlength variations due to coiling of said strip, the convolutions of saidstrip portions defining two spirally intercalated internal filterchambers one of which is open in the region of said free edges andclosed in the region of said second edges due to said strip portionsbeing folded and therefore unitary along said second edges; and meansfor closing the other of said intercalated internal filter chambersalong said free edges of said strip portions, so that said intercalatedinternal filter chambers are open and closed along opposite edge of saidstrip portions, respectively.
 2. A filter element as defined in claim 1,said one strip portion including a marginal section extending along saidfree edge and folded back upon a corresponding section of said one stripportion.
 3. A filter element as defined in claim 1, said one stripportion facing inwardly toward the center of the coiled strip and theother of said strip portions facing outwardly away from said center. 4.A filter element as defined in claim 3, said one strip portion includinga marginal section extending along said free edge and folded back upon acorresponding section of said one strip portion so as to be locatedbetween the latter and the other of said strip portions.
 5. A filterelement as defined in claim 1, wherein the combined cross-sectional areaof said open end of said other corrugations exceeds the combinedcross-sectional area of said open ends of said some corrugations.
 6. Afilter element as defined in claim 1, said corrugations forming in theregion of said free edge of said one strip portion a uniformly sinuousconfiguration.
 7. A filter element as defined in claim 1; furthercomprising a tuBular center element about which said strip isconvoluted; and adhesive means sealingly connecting the initialconvolution of said strip with said center element.
 8. A filter elementas defined in claim 7, wherein said adhesive means is thermoplasticmeans sealingly connecting said initial convolution with said centerelement at the opposite axial ends thereof.
 9. A filter element asdefined in claim 7, wherein said tubular center element is a cardboardtube.